Preheat the oven to 350°F (175°C)
Line baking sheets with parchment paper
Whisk together 1 1/4 cups all-purpose flour, 1/2 cup unsweetened cocoa powder, 1 teaspoon baking soda, and 1/2 teaspoon salt
In a separate bowl, beat 1/2 cup softened unsalted butter, 1/2 cup granulated sugar, and 1/2 cup packed brown sugar until creamy
Add 1 large egg and 1 teaspoon vanilla extract, then mix until combined
Gradually add the dry ingredients to the wet ingredients and mix until just combined
Stir in 1 to 1 1/2 cups chocolate chips
Scoop dough onto the prepared baking sheets
Bake for 9 to 11 minutes
Let cookies cool on the baking sheet for 5 minutes
Transfer cookies to a wire rack to cool completely